relax the anti-amplification byte count
relax the anti-amplification byte count

Before we would only consider bytes of valid QUIC packets to limit the
amount of sent bytes before address validation, however this is way too
strict, as to avoid amplification we just need to count *any* bytes
received from clients.

Notably Firefox pads Initial packets at the datagram level, rather than
within QUIC packets, which would appear to us as invalid packets so
wouldn't be counted towards the anti-amplification allowance.

cloudflare/quiche,cloudflare/quiche,cloudflare/quiche